1. Field of the Invention:
The present invention relates to a seal for a damper used in a motor vehicle suspension.
2. Description of the Relevant Art:
Dampers are widely used in suspensions on automobiles, motorcycles, and other motor vehicles for dampening shocks imposed from surface irregularities of a road on the motor vehicle while it is traveling on the road.
Various dampers for use in motor vehicle suspensions are known in the art. One principal damper construction comprises a cylinder connected to a motor vehicle body or a wheel axle and a piston rod movably disposed in the cylinder and connected to the wheel axle or the motor vehicle body. The piston rod is secured to a piston disposed in the cylinder and slidably held against the inner peripheral surface of the cylinder, the piston dividing the inner space of the cylinder into two oil chambers, for example. When the motor vehicle travels on a road, the piston and the cylinder are vertically moved with respect to each other as the wheel goes over road surface irregularities. The volumes of the oil chambers are caused to vary, forcing the oil to flow between the oil chambers through orifices defined in the piston. Since the orifices impose resistance to the flow of the oil therethrough, the relative movement of the piston rod and the cylinder is restricted to dampen shocks applied by the road to the motor vehicle body.
Inasmuch as the piston rod is displaced with respect to the cylinder, a seal is mounted in the cylinder at its open end in surrounding relation to the piston rod for preventing the oil from leaking out of the cylinder along the peripheral surface of the piston rod.
A typical seal is disclosed, for example, in U.S. Pat. No. 4,203,507 issued May 20, 1980 to Tomita et al. The patented seal comprises an annular elastomeric body of rubber or the like. The seal includes an outer attachment flange for attachment to a bushing or the like mounted in a cylinder and an inner contacting web for contact with a piston rod. A rigid reinforcing metal member is embedded in the attachment flange for allowing the seal to be securely attached to the bushing. The reinforcing metal member extends from one end of the attachment flange all the way to the other end thereof. The inner contacting web has a plurality of of lips on its inner peripheral surface, the lips being pressed against the outer peripheral surface of the piston rod by rings forcibly fitted over the outer peripheral surface of the inner contacting web.
When the damper is operated, the piston rod is displaced with respect to the cylinder and hence the seal at all times irrespective of the magnitude of shocks transmitted from road surface irregularities to the damper. Where road surface irregularities are smaller, the piston rod is displaced relatively to the cylinder through smaller strokes and more frequently.
It is known that when the piston rod is displaced relatively to the seal, a transient occurs from a static friction mode to a dynamic friction mode. If the piston rod stroke is smaller and more frequent, i.e., if the damper is in a higher-frequency, smaller-amplitude range, then the transient between the static and dynamic friction modes takes place many times within a short period of time. This causes the piston rod to stick to the cylinder, whereupon vibrations from the road surface are transmitted via the damper to the motor vehicle body, thus lowering the riding comfort.